Engine piston and method of making the same



W. SIEMAN, JR

ENGINE PISTON AND METHOD OF MAKING THE SAME Aug. 25, 1931.

2 Sheets-Sheet 1 Filed Nov. 22, 1928 Aug. 25, 1931. w. SIEMAN, JR 1,820,253

ENGINE ns'ron AND METHOD OF MAKING THE sum Filed Nov. 22, 192 2 Sheets-Sheet 2 /0 1/06 ie LS2 f o o Patented Aug. 25, 1931 WILLIAM SIEMAN, JR., OF MENOMINEE, MICHIGAN ENGINE PISTON AND METHOD OF MAKING THE SAME Application filed November 22, 1928. Serial No. 321,077.

This invention relates to improvements in engine pistons and method of making the same and it consists of the matters hereinafter described and more particularly pointed out in the appended claims.

The primary object of the invention is to provide a piston, which may be more readily and easil fitted to the associated engine cylinder, t us eliminating to a great extent the skill necessary for the proper fitting of piston and cylinders as now made.

Another object of the invention is to provide a piston which requires less breaking in time when installed in a cylinder and one which will not pump oil because of its action or tendency to automatically expand or enlarge circumferentially at the skirt, to compensate for any wear that there takes place so that the piston becomes self fitting.

Another object of the invention is to improve the method of making such pistons, whereby a leeway in tolerances heretofore recognized as standard is possible without sacrificing uniformity and accuracy, whereby production is increased without waste.

The above mentioned objects of the invention, as well as others, together with the many advantages thereof, will more fully appear as I proceed with my specification.

In the drawings Fig. 1 is a view partly in side elevation and partly in section of a piston blank or casting before any of the steps of my improved method has been carried out thereon.

Fig. 2 is a view similar to Fig. 1 after the piston casting thereof has been circumferentially slotted and the. piston skirt has been longitudinally slotted.

Fig. 3 is a horizontal section through the piston as taken on the line 3-3 of Fig. 2.

Fig. 4 is a view similar to Fig. 3 after the skirt portions on each side of the longitudinal slot have been drawn closer together and out of round to make it eccentric.

Fig. 5 is a perspective view of a certain sleeve embodied in the improved piston.

Fig. 6 is a longitudinal sectional view through the finished piston, minus the usual rings, as taken in the plane of the wrist pin bosses.

Fig. 7 is another longitudinal sectional view through the piston as taken on the line 77 of Fig. 6. I

Fig. 8 is a horizontal sectional view through the finished piston as taken on the line 88 of Fig. 6.

Fig. 9 is a diagrammatic view showing the various steps of operating upon the piston skirt.

In carrying out my improved method of making the finished piston, which is selffitting in the associated cylinder, I start with a piston blank or casting, preferably of aluminum and of a diameter oversize with respect to the bore of the cylinder in I which it is used. Such a blank or casting, as best shown in Fig. 1, comprises a tubular body 1 closed at one end by a top wall 2. On opposite sides of the inner surface of the tubular body are diametrically arranged, horizontally disposed bosses 3-3 which in the finished piston provide the usual wrist pin bosses, the same being located about midway between the ends of the piston as is customary in pistons for internal combustion engines.

Above each boss 3 the adjacent part of the tubular body is made of a greater thick ness as at 4 and said part is of a width ap proximating the diameter of the associated boss, a vertically extending rib 5 being formed in said thickened part 4 which terminates at one end at said boss and at its other end at approximately the top wall 2.

In a plane at substantially a right angle to the plane of the Wrist pin bosses 33 on the inner surface of one side of the tubular body is provided a flat rib 6 which extends from the bottom edge of the body to a plane or point above that of said bosses 3-3.

On that side of the'body opposite said flat rib on the inner surface thereof are top and bottom pairs of laterally spaced bosses 77 and on the outside of said wall in one of each pair of bosses is a recess8. The bosses 77 of each pair are drilled from the recess side to receive a certain bolt or screw as will later appear.

In a'piston blank of the construction above described and which as before stated is over- 10s size in diameter with reference to the bore of the cylinder in which it is to be used, I cut an annular slot 9 therein in a plane above the wrist pin bosses and approximate ly midway between the said bosses and wall 2. This slot may be easily cut in a lathe and extends clear through and around the body part but not through the thickened parts 4 which together with the ribs 5 form posts 1 connecting the top and bottom parts of the piston together. Instead of cutting said slot 9 as described, the same may be formed in the piston blank at the time the same is cast.

For the sake of convenience, all of the piston above the slot will hereinafter be referred to as the head 10 and all of the piston below the slot will be referred to as the skirt 11 as best indicated in Fig. 2, the only two points of connection between the head and skirt being the posts 4 before mentioned.

I next produce a longitudinal slot 12 in that part of the skirt, midway between the bosses of the pairs of bosses 7-7, said slot extending from the top to the bottom of the skirt. In a piston of 4 inch diameter, the slot 12 will be about 3/16 of an inch wide, these dimensions being merely illustrative and not absolutely fixed ones as is apparent. With the skirt longitudinally slotted as described it is apparent that the margins of the skirt along the slot 12 are capable of being drawn toward each other by'means as will later appear, the skirt of the piston yielding or flexing circumferentially from each side of the fiat rib (5 so that said skirt will be out of round but will have an inherent tendency to expand or enlarge.

To bring the said margins toward each other I provide the following mechanism. 13 indicates a bolt, one associated with each pair of bosses 77 on the inside of the skirt on opposite sides of the slot 12. Said bolt has a head 13 and the threaded end of the bolt is inserted into one boss 7 of one pair from the recess 8 to extend and be threaded into the other or associated boss '7. In inserting the bolt in the bosses of each pair, I place a pair of sleeves 1114 upon each bolt. one of such sleeves being best shown in Fig. 5. Each sleeve has an annular shoulder 15 near its outer end and a relatively stifi' helical expansion spring .16 surrounds said sleeves and abuts at its ends against the shoulders 15--15, the said sleeves being urged away from each other and into engagement with the flat face or shoulders of the bosses 7-7. By drawing up on these two bolts the margins of the skirt on each side of the slot' 12 are drawn toward each other, the spring being thereby placed under tension. Thus the springs 16 assist in increasing the tendency of the skirt to circumferentially expand or enlarge. I draw the skirt margins together until the slot 12 is only about a 1/32 inch wide and then lock the bolt in place by a cotter pin 17 passing through the relatively small bore 18?) in the head 13a and extending into the relatively large opening 17a as best shown in Fig. 4;. When said skirt margins are drawn together, the skirt will be out of' round or eccentric as best illustrated by a comparison of the full and dotted lines a and I) in Fig. 9, the skirt being of a major diameter in the plane of the wrist pin bosses 3 and of minor diameter in the plane of the slot 12 and flat rib 6. In this respect it is pointed out that in the finished piston the flat rib 6 balances the margins of the skirt adjacent the slot, together with the parts associated therewith.

Thereafter I turn down the skirt in a lathe to make it perfectly round again and of a diameter equaling that of the beforementioned minor diameter, more metal being removed from those sides of the skirt in the planes of the wrist pin bosses than from the sides in the plane of the flat rib 6 and slot 12. Thus the skirt becomes perfectly round again as indicated by the dot and dash lines 0 in said Fig. 9. In this turning down of the skirt, the head 10 may also be operated upon to turn it down to size and at the same time form the compression ring grooves 10 as well as the oil ring groove 10 therein. The piston is then drilled to provide the oil return passages 10 after which the wrist pin bosses may be drilled and reamed as at 3 in Fig. 6 to receive the usual wrist pin for the connecting rod.

It is apparent from the above that when the margins of the skirt on each side of the slot are drawn toward each other that the skirt is placed under circumferential tension and has the inherent tendency to enlarge and return to its original and normal condition, the bolt 13 acting to limit the amount of such enlargement. Thus when the finished piston is in a cylinder the skirt will. naturally tend to expand or enlarge circumferentially and open up and this tendency is augmented by the springs 16 with the result that the skirt snugly and accurately fits the cylinder bore and acts in the nature of an extra and wider ring to assist in retaining compression and preventing the pumping of oil.

By reason of the skirt construction mentioned the piston may be more easily inserted or assembled into the associated cylinder bore as a greater tolerance in clearance is provided for, which clearance is automatically taken up as the piston fits itself to the bore. Such a piston, having a more perfect initial fit with respect to the cylinder bore, readily works itself into full complemental engagement with said bore so that the breaking in time of a new engine is materially reduced.

Again, the head can be made more undersize than is otherwise possible so that under expansion due to great temperatures such as met with in automobile engines the head cannot so expand asto come intodirect engagement with the cylinder bore and there stick or freeze.

While in describing my invention I have referred in detail to the form, construction and arrangement of the various parts thereof, as well as to the various steps in the making of the piston, the same is to be considered merely as illustrative so that I do not wish to be limited thereto except as may be specifically pointed out in the appended claims.

I claim as my invention I 1. A piston comprising a head and skirt, said skirt provided with a longitudinal slot, pairs of bosses on either side of the slot and located on the inside of the skirt, the bosses on one side of the slot provided with a threaded bore with the bosses on the other side of the slot provided with bores connecting with recesses in the outer wall of the piston, threaded bolts passing transversely of the slot in the skirt and through the bores in the bosses on one side ofthe slot with their headed ends located in the recesses in the piston wall andwith their threaded ends screwed into the threaded bores in the bosses on the opposite side of the slot, cotter pins passing through bores in the heads of the bolts and projecting through larger openings in the walls of the recesses, and expansible springs encircling the bolts to assist in enlarging the skirt.

2. A piston comprising a head and skirt, said skirt provided with a longitudinal slot and having an inherent circumferential eularging tendency, a pair of bosses on either side of the slot and located on the inside of the skirt, the boss on one side of the slot provided with a threaded bore, the boss on the other side of the slot provided with a bore connecting with a recess in the outer wall of the piston, a threaded bolt passing transversely of the slot in the skirt and through the bore in the boss on one side of the slot with its threaded end screwed into the threaded bore in the boss on the other side of the slot, the head of the bolt being located in the recess in the outer wall of the piston, a cotter pin for preventing rotation of the bolt, and a spring encircling the bolt and assisting the skirt in its inherent circumferential enlarging tendency.

- 3. A piston comprising a head and skirt, said skirt provided with a longitudinal slot and having an-inherent circumferential enlarging tendency, a pair of bosses on either side of the slot and located on the inside of the piston, the boss on one side of the slot provided with a threaded bore, the bosson the other side of the slot provided with a bore connecting with a recess in the outer wall of the piston, the bores of the two bosses being in alignment and coaxial, a threaded bolt transversely of the slot passing through the bore in the boss on one side of the slot with its threaded end screwed into the threaded bore in the boss on the other side of the slot, the head of the bolt being located in the recess in the outer wall of the piston, means for preventing rotation of the bolt and a spring encircling the bolt and assisting the skirt in its inherent circumferential enlarging tendency.

In testimony whereof, I have hereunto set my hand, this 17th day of November,

WILLIAM SIEMAN, JR. 

